ipv4: save cpu cycles from check_leaf()

Compiler is not smart enough to avoid double BSWAP instructions in
ntohl(inet_make_mask(plen)).

Lets cache this value in struct leaf_info, (fill a hole on 64bit arches)

With route cache disabled, this saves ~2% of cpu in udpflood bench on
x86_64 machine.
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/fib_trie.c

@@ -110,9 +110,10 @@ struct leaf {
 
 struct leaf_info {
 	struct hlist_node hlist;
-	struct rcu_head rcu;
 	int plen;
+	u32 mask_plen; /* ntohl(inet_make_mask(plen)) */
 	struct list_head falh;
+	struct rcu_head rcu;
 };
 
 struct tnode {
@@ -451,6 +452,7 @@ static struct leaf_info *leaf_info_new(int plen)
 	struct leaf_info *li = kmalloc(sizeof(struct leaf_info),  GFP_KERNEL);
 	if (li) {
 		li->plen = plen;
+		li->mask_plen = ntohl(inet_make_mask(plen));
 		INIT_LIST_HEAD(&li->falh);
 	}
 	return li;
@@ -1359,10 +1361,8 @@ static int check_leaf(struct fib_table *tb, struct trie *t, struct leaf *l,
 
 	hlist_for_each_entry_rcu(li, node, hhead, hlist) {
 		struct fib_alias *fa;
-		int plen = li->plen;
-		__be32 mask = inet_make_mask(plen);
 
-		if (l->key != (key & ntohl(mask)))
+		if (l->key != (key & li->mask_plen))
 			continue;
 
 		list_for_each_entry_rcu(fa, &li->falh, fa_list) {
@@ -1394,7 +1394,7 @@ static int check_leaf(struct fib_table *tb, struct trie *t, struct leaf *l,
 #ifdef CONFIG_IP_FIB_TRIE_STATS
 				t->stats.semantic_match_passed++;
 #endif
-				res->prefixlen = plen;
+				res->prefixlen = li->plen;
 				res->nh_sel = nhsel;
 				res->type = fa->fa_type;
 				res->scope = fa->fa_info->fib_scope;
@@ -1402,7 +1402,7 @@ static int check_leaf(struct fib_table *tb, struct trie *t, struct leaf *l,
 				res->table = tb;
 				res->fa_head = &li->falh;
 				if (!(fib_flags & FIB_LOOKUP_NOREF))
-					atomic_inc(&res->fi->fib_clntref);
+					atomic_inc(&fi->fib_clntref);
 				return 0;
 			}
 		}